Shell has reportedly shut down a key oil pipeline in Nigeria to stop a leak caused by oil theft.

The 97 kilometre long Nembe Creek Trunkline is said to carry around 150,000 barrels of oil a day and has previously been closed several times following oil thefts.

Precious Okolobo, a spokesman of Shell Petroleum Development Co. of Nigeria is reported as saying: “We closed the Nembe Creek Trunkline… for the removal of crude theft points. We plan to complete the exercise and reopen the line as soon as possible.”

Crude oil theft is believed to be a major problem in Nigeria, with estimates the nation loses around $6 billion in revenue every year as a result.

Nigeria is Africa’s largest producer of oil, accounting for more than two million barrels per day.